Through more than 100 years' development and modification, the mechanical efficiency of internal combustion engine almost reaches its extremity. With the aid of electronic technology in recent years, the combustion efficiency is increased, while the work efficiency is difficult to increase due to the limit of the inherent working mode, the reasons include:
1. The internal combustion engines operate in a constant volume working mode since they are invented, that is to say, in a theory cycle of the existing internal combustion engines, the four strokes of intake, compression, combustion, exhaust are isometric (equal-stroke); the combustion working stroke of the piston is equal to the intake stroke (the working volume of the cylinder is equal to the intake volume). Therefore, at the end of combustion working, the temperature and pressure of the combustion gas in the cylinder are still high, and the exhaust gas is discharged in flame form. The heat loss caused by this constant volume expansion working and high temperature exhausting mode accounts for approximately 35% of the total heat. This is inevitable for the existing internal combustion engines, because the structure of the existing internal combustion engine determines that the working volume of the cylinder is equal to the intake volume (Since the exhaust advance angle is 50°-60°, the limited working stroke is further reduced, and actually the working stroke is shorter than the intake stroke). The high temperature exhausting phenomenon is caused by the fact that the piston can not do work continuously after reaching the bottom dead point, and the exhaust gas which still contains massive heat energy only can be discharged as waste gas.
2. In order to avoid the overheating phenomenon of internal combustion engine appearing, it is necessary to cool the cylinder body by forced circulation cooling, and the heat carried off by the cooling system accounts for approximately 30% of the total heat. According to operation principle of high temperature exhausting, the internal combustion engine operating in the constant volume working mode can not improve its heat efficiency even though a heat preservation and heat insulation means is applied to increase the operating temperature and as a result the exhaust temperature is increased, because there is no essential modification in the heat energy conversion mode, so that the heat energy which is not carried off by the cooling system will be carried off by the exhaust system.
3. The existing internal combustion engines include spark-ignition internal combustion engines and compression-ignition internal combustion engines, and the compression ratio is used to indicate the compression degree of gas when the piston reaches the compression end. The compression ratio is quite low for the early internal combustion engines, it is 5-8:1 in the spark-ignition internal combustion engine, and 10-18:1 in the compression-ignition internal combustion engine, so the heat efficiency is low. In recent years, the compression ratio is increased to 8-11:1 for the spark-ignition internal combustion engines, corresponding to a compression degree of about 0.7-1 Mpa, and to 16-22:1 for the compression-ignition internal combustion engines, corresponding to a compression degree of about 1.5-2 Mpa, so the heat efficiency is improved remarkably. Obviously the magnitude of the compression ratio is in close correlation with the heat efficiency of the internal combustion engines, the reason is that a higher compression ratio can produce a higher combustion temperature and pressure, and the average working pressure on the piston is increased, therefore the heat efficiency is increased. However, the compression ratio of the existing internal combustion engine is difficult to be further increased due to the restriction of the detonation phenomenon and the mechanical structural strength of the internal combustion engine.
4. The theoretical compression ratio of the existing internal combustion engine is fixed. When running in an operating condition of low rotational speed and heavy load (namely with the maximum air intake quantity), the internal combustion engine may reach its designed compression degree. While running in an operating condition of high rotational speed and light load (namely with a small air intake quantity), the actual compression degree reduces at the top dead point even though the theoretical compression ratio is not changed, thereby the heat efficiency reduces. Therefore the heat efficiency is quite different in different operating conditions. This is the main reason why the heat efficiency of substance-controlling internal combustion engine is higher than that of the quantity-controlling internal combustion engine.
5. In the existing internal combustion engine, the ignition or oil injection time is set about 20°-30° before the top dead point, and the mixed gases enter the main combustion period after a physical and chemical reaction process. The highest combustion temperature and pressure occur at about 6° behind the top dead point by controlling the ignition time. In fact the produced temperature and pressure in this range are only related to the concept of strength in spite of how high they are. When passing through the vicinity of top dead point, the pressure is the highest but the speed of piston is almost “zero”, therefore it does a little work. Furthermore, it is inevitable that the combustion gas leaks out through the piston ring. In this stage, heat quantity is concentrated, the temperature is the highest, and the heat loss also is the most. So the leaked “substance” at this time is not neglectable. For example, when treading the bicycle, make an effort it is of no use no matter how you put forth your strength on the peak of the footboard (corresponding to the top dead point), and only after turning to a certain angle, it is able to produce a force moment for doing work. In view of this fact, the ignition time of the internal combustion engine should be postponed to let the highest combustion temperature and pressure occur about 15° behind the top dead point.
The existing internal combustion engine is ignited or injected oil in advance in all operating conditions, so that a part of fuel begins to burn before the top dead point, and heat energy is released to elevate the temperature and the pressure rapidly. Thereby the compression negative work is increased, and it is likely to cause the detonation phenomenon which makes the operation to be wild. The basic reason that the existing internal combustion engine does not postpone the ignition and oil injection is that, only at the top dead point the compression degree and the constant volume degree are the highest, and the combustion temperature and the pressure are the highest. It is the best ignition time but not the best working time, the best working time is 15° behind the top dead point, so the ignition time should be postponed. But the postponement of the ignition may lead to decrease of the compression degree and the constant volume level, and the unburned gas expands as the piston runs down after the piston passes through the top dead point, thereby the compression degree is reduced and the heat efficiency is reduced.
In view of the above phenomenon, many technical solutions appeared one after another, such as Chinese patent CN1417463A, CN1388307A and so on, all of them proposed that based on the original internal combustion engines, modification is made without changing the original structure, the working stroke of the piston is increased by reducing the intake quantity or increasing the working volume of the cylinder, so as to reach the effect of saving fuel, the method of reducing intake quantity includes: (1) perform with throttling of the throttle. (2) perform with closing intake valve in advance in the inspiration process. (3) perform by opening the exhaust valve at the beginning of the compression stroke and closing the exhaust valve after a part of the air exhausted, and so on.
These solutions may save fuel theoretically, for the reason that after the intake quantity of the cylinder is reduced, that is to say the working substances in the cylinder is reduced, at the beginning stage of working (i.e. constant volume working stage) the original combustion temperature and pressure is maintained, at the latter stage of working (desired to obtain gain stage, theoretically there is 30%-35% heat energy in the combustion gas in this stage) there is massive heat energy in the gas of the cylinder, the question is the grade of the heat energy is very low, the work actually can be obtained is very little (only if adopted means to promote its grade). The key point is that the total heat is also reduced after the working substance entering the cylinder is reduced, and the area of dissipation of the cylinder is increased, the heat dissipating capacity is relatively increased, though there is pressure in the gas in the cylinder that cooled by the water jacket but it can not efficiently work, the work obtained by the theoretically increased stroke counteracts with the mechanical loss, especially in case of high rotational speed and high efficiency operating condition then the negative work exceeds positive work and obtains more less than gains. Therefore, it is inadequate to merely depending on reducing intake quantity or increasing the stroke of the piston, thus the improved internal combustion engine is inevitably led to under power and lose the practical value.